Create a bash function in Dockerfile, and use it to download static compile wget.
Does you use Dockerfile like this?
# install wget
RUN apt-get update && apt-get install -qq -y --no-install-recommends wget && rm -rf /var/lib/apt/lists/*
#####################
# do whatever tasks which need wget to download somethings ...
######################
# remove wget
RUN apt-get purge -y --auto-remove wget
This is not the correct way to do this.
If run docker history your_image, you will see
...
41753cb4a6be 4 hours ago /bin/sh -c apt-get purge -y --auto-remove ... 445 kB
1eae68198132 17 hours ago /bin/sh -c apt-get update && apt-get insta... 34.4 MB
...Because you install wget and remove wget in seperate step, you got about 34MB unuseful data
into docker layout, in other word, you image size get bigger.
Another way CORRECT way to do this is, in every step you need wget, write as followings
RUN apt-get update && apt-get install -qq -y --no-install-recommends wget && rm -rf /var/lib/apt/lists/* && \
do-whatever-process-need-wget && \
RUN apt-get purge -y --auto-remove wgetThis method is good, but too much redundant code, not perfect.
ADD some_static_wget_url/static_get /usr/local/bin/wget
RUN chmod +x /usr/local/bin/wgetThis is the way i currently use, only one problem, we have to download this wget again and again
when build image, And, same file is saved to two layer in docker as in report by docker history.
d266e671e16f About a minute ago /bin/sh -c chmod +x /usr/local/bin/wget 618 kB
56d3e171fa7c About a minute ago /bin/sh -c #(nop) ADD tarsum.v1+sha256:e32... 618 kBThis project is the attempt to do this, following is a example dockerfile
FROM ruby:2.3-slim
MAINTAINER Billy Zheng(zw963) <vil963@gmail.com>
RUN bash -c 'function __wget() { \
local URL=$1; \
read proto server path <<<$(echo ${URL//// }); \
local SCHEME=${proto//:*} PATH=/${path// //} HOST=${server//:*} PORT=${server//*:}; \
[[ "${HOST}" == "${PORT}" ]] && PORT=80; \
exec 3<>/dev/tcp/${HOST}/${PORT}; \
echo -en "GET ${PATH} HTTP/1.1\r\nHost: ${HOST}\r\nConnection: close\r\n\r\n" >&3; \
local state=0 line_number=0; \
while read line; do \
line_number=$(($line_number + 1)); \
case $state in \
0) \
echo "$line" >&2; \
if [ $line_number -eq 1 ]; then \
if [[ $line =~ ^HTTP/1\.[01][[:space:]]([0-9]{3}).*$ ]]; then \
[[ "${BASH_REMATCH[1]}" = "200" ]] && state=1 || return 1; \
else \
printf "invalid http response from '%s'" "$URL" >&2; \
return 1; \
fi; \
fi; \
;; \
1) \
[[ "$line" =~ ^.$ ]] && state=2; \
;; \
2) \
echo "$line"; \
esac \
done <&3; \
exec 3>&-; \
}; \
__wget http://202.56.13.13/base64_encoded_static_wget |base64 -d > /usr/local/bin/wget; \
if [ -s /usr/local/bin/wget ]; then \
chmod +x /usr/local/bin/wget; \
else \
echo "Network is not connected?" >&2; \
exit 1; \
fi;'
CMD ["ruby"]When it build, we can see docker history image_name
9d95c852997c 31 seconds ago /bin/sh -c bash -c 'function __wget() { l 618.3 kB Only 618.3 KB is added into new build image, and we almost save 35MB space compare to first method.
And, we no need download it again and again when next build.
this static_wget is got from minos-static project,
what i does is just:
- download static compiled wget, and pack with
upx(size from 1.5M reduce to 604kb) - create
__wgetfunction in Dockrfile, please refer to this StackExchange answer, and this, for a complete example, please see this - encode wget binary with base64, because
__wgetfunction not full-suppot binary data transfer. - save
base64 encoded static compiled wgetin some place which not needhttps, because__wgetnot support. - use
_wgetfunction to download wget.